Add Spotify integration with toggleable music source

- Add OAuth 2.0 PKCE authentication for Spotify Web API
- Create SpotifyNowPlayingMonitor for polling current track
- Add Settings tab with music source toggle (Apple Music/Spotify)
- Store tokens securely in Keychain
- Display current track on Glass as NOW_PLAYING card

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

IrisCompanion/iris/Orchestrator/ContextOrchestrator.swift

@@ -26,6 +26,15 @@ final class ContextOrchestrator: NSObject, ObservableObject {
     @Published private(set) var lastFetchFailed: Bool = false
     @Published private(set) var musicAuthorization: MusicAuthorization.Status = .notDetermined
     @Published private(set) var nowPlaying: NowPlayingSnapshot? = nil
+    @Published private(set) var spotifyNowPlaying: SpotifyNowPlaying? = nil
+    @Published var musicSource: MusicSource = .appleMusic {
+        didSet {
+            if oldValue != musicSource {
+                switchMusicMonitor()
+                UserDefaults.standard.set(musicSource.rawValue, forKey: "music_source")
+            }
+        }
+    }
 
     private let logger = Logger(subsystem: Bundle.main.bundleIdentifier ?? "iris", category: "ContextOrchestrator")
 
@@ -38,6 +47,8 @@ final class ContextOrchestrator: NSObject, ObservableObject {
     private let server: LocalServer
     private let ble: BlePeripheralManager
     private let nowPlayingMonitor = NowPlayingMonitor()
+    private let spotifyMonitor: SpotifyNowPlayingMonitor
+    private let spotifyAuth: SpotifyAuthManager
 
     private var lastRecomputeLocation: CLLocation? = nil
     private var lastRecomputeAccuracy: CLLocationAccuracy? = nil
@@ -46,11 +57,20 @@ final class ContextOrchestrator: NSObject, ObservableObject {
 
     init(store: FeedStore = FeedStore(),
          server: LocalServer = LocalServer(),
-         ble: BlePeripheralManager) {
+         ble: BlePeripheralManager,
+         spotifyAuth: SpotifyAuthManager) {
         self.store = store
         self.server = server
         self.ble = ble
+        self.spotifyAuth = spotifyAuth
+        self.spotifyMonitor = SpotifyNowPlayingMonitor(authManager: spotifyAuth)
         self.ranker = HeuristicRanker(lastShownAt: { id in store.lastShownAt(feedItemId: id) })
+
+        if let savedSource = UserDefaults.standard.string(forKey: "music_source"),
+           let source = MusicSource(rawValue: savedSource) {
+            self.musicSource = source
+        }
+
         super.init()
 
         locationManager.delegate = self
@@ -73,13 +93,21 @@ final class ContextOrchestrator: NSObject, ObservableObject {
 
         nowPlayingMonitor.onUpdate = { [weak self] update in
             Task { @MainActor in
-                guard let self else { return }
+                guard let self, self.musicSource == .appleMusic else { return }
                 self.musicAuthorization = update.authorization
                 self.nowPlaying = update.snapshot
                 self.pushLatestFeedToBle()
             }
         }
 
+        spotifyMonitor.onUpdate = { [weak self] update in
+            Task { @MainActor in
+                guard let self, self.musicSource == .spotify else { return }
+                self.spotifyNowPlaying = update.snapshot
+                self.pushLatestFeedToBle()
+            }
+        }
+
         let feed = store.getFeed()
         lastFeed = feed
     }
@@ -88,7 +116,7 @@ final class ContextOrchestrator: NSObject, ObservableObject {
         authorization = locationManager.authorizationStatus
         logger.info("start auth=\(String(describing: self.authorization), privacy: .public)")
         server.start()
-        nowPlayingMonitor.start()
+        startMusicMonitor()
         requestPermissionsIfNeeded()
         locationManager.startUpdatingLocation()
     }
@@ -96,6 +124,27 @@ final class ContextOrchestrator: NSObject, ObservableObject {
     func stop() {
         locationManager.stopUpdatingLocation()
         nowPlayingMonitor.stop()
+        spotifyMonitor.stop()
+    }
+
+    private func startMusicMonitor() {
+        switch musicSource {
+        case .appleMusic:
+            nowPlayingMonitor.start()
+        case .spotify:
+            spotifyMonitor.start()
+        }
+    }
+
+    private func switchMusicMonitor() {
+        nowPlayingMonitor.stop()
+        spotifyMonitor.stop()
+        nowPlaying = nil
+        spotifyNowPlaying = nil
+
+        startMusicMonitor()
+        pushLatestFeedToBle()
+        logger.info("Switched music source to \(self.musicSource.rawValue)")
     }
 
     func recomputeNow(reason: String = "manual") {
@@ -500,7 +549,15 @@ final class ContextOrchestrator: NSObject, ObservableObject {
     }
 
     private func feedForGlass(base: FeedEnvelope, now: Int) -> FeedEnvelope {
-        guard let nowPlayingCard = nowPlaying?.asFeedItem(baseGeneratedAt: base.generatedAt, now: now) else {
+        let nowPlayingCard: FeedItem?
+        switch musicSource {
+        case .appleMusic:
+            nowPlayingCard = nowPlaying?.asFeedItem(baseGeneratedAt: base.generatedAt, now: now)
+        case .spotify:
+            nowPlayingCard = spotifyNowPlaying?.asFeedItem(baseGeneratedAt: base.generatedAt, now: now)
+        }
+
+        guard let nowPlayingCard else {
             return base
         }